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Introduction to Central Evaporative Air Cooling Plant
In the previous articles of this series we saw DX and Chilled types of central air conditioning plants. In these plants the regular refrigeration cycle is used comprising of components like compressor, condenser, expansion valve and the cooling coil or evaporator. The central air washer is nothing but an evaporative or desert cooler. The small desert cooler is used for rooms and halls, just like the window and split air conditioners. Its elder brother, the central cooler is used for cooling the whole building just like the central air conditioning plants. Just as the central air conditioner has all components similar to the window or split AC, the central air washer has the components similar to the desert coolers.
All the components of the central air washer are enclosed in the box which is also called as the air handling unit. In this unit the water is sprayed from the spray nozzles. There is a large blower that sucks the atmospheric air and blows it over the spray of water. As the air flows over the water, the particles of water absorb heat from the air and get evaporated. Due to loss of heat the temperature of air reduces and it gets humidified. The cool and humidified air leaves the washer and enters rooms to be cooled via the ducts. The whole air washer unit should be kept in open space so that fresh air can be absorbed continuously.
All the important components of central air washer are discussed below:
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Parts of the Central Air Washer or Central Evaporative Air Cooler
1) Water Tank: The water tank is located at the bottom of the air washer. It is connected to the water pipe from suitable source for continuous supply of water. The central air washers need large quantities of water, which increases as the number of rooms to be cooled increases. For proper performance of the central air washer one has to ensure abundant supply of water continuously. The water in the water tank can be ordinary water or it can be chilled water. Usually ordinary water is used.
2) Spray nozzles: The water from the water tank is pumped to the spray nozzles via plastic or mild steel piping. The spray nozzles spray the water inside the central air washer.
3) Water pump: The water pump pumps the water from water tank to the spray nozzles. It is the heart of the central evaporative cooling system.
4) Blower: The blower sucks the atmospheric air and blows it over the spray of water. During this process the particles of water get evaporated as they absorb heat from the air. Due to loss of heat the temperature of atmospheric air reduces and its humidity increases. The air at low temperature and high humidity enters the rooms to be cooled via the ducts.
5) Air filter: Air filter is placed towards the external part of the box of the air washer. This ensures that the air sucked by the blower gets filtered before finally entering into the rooms.
6) Ducts: Ducts are laid from the air washer to all the rooms of the building that are to be cooled. The ducts end in the diffuser that delivers the chilled air to the rooms.
The central evaporative cooling systems are highly effective in hot and dry climates. One can get excellent cooling effect similar to the air conditioning systems from these units. While the central air conditioning plants have very high initial and running costs, these costs of the central evaporative cooler are meager since there is no compressor, the most expensive and most power consuming unit of the central air conditioning plant. The central evaporative air cooling plants is an excellent alternative to the central air conditioning plant in suitable conditions.
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Central Air Washer or Central Evaporative Air Cooling Plant
There are two types of central air conditioning systems: Direct Expansion (DX) type of central air condition plants and Chilled Water type of the central air conditioning plants. In this series of articles both these plants and air handling units have been described.